The second world war was one of the major key factors that changed the structures in politics across the world and contributed to decline of colonialism. Here’s how:

-Weakening of European Powers: There whose economies and military were greatly stretched and crippled by the war were the major European colonial powers namely Britain, France and Netherlands. They failed in the way they could not exercise authority and had not the power and political will to continue to hold and control huge overseas territories due to internal pressured and emergence of nationalist movements.
-Rise of New Powers: Second, an unprecedented global war was observed wherein two super powers, the United States and the Soviet Union emerged during the war. These new powers demanded national self- determination, decolonization; all of which contributed to the further breaking of European empires’ hold.
-Growth of Nationalist Movements: The war, therefore, offered a boost to anti-colonialism in Asia and or Africa. The colonial subjects, who played a crucial role with the colonial masters during the same fights for liberation and wanted to govern themselves.
-Ideological Change: The war led to shift of ideology to self determination and human rights. Another cause was the Atlantic Charter that announced people had the right to choose the type of the governmental system themselves; therefore, colonialism was not legitimate.

Thus, the war offered the latter an environment for decolonization . While sometimes a long process and sometimes even involving conflicts, this led to the disintegration of most colonial empires and transition to the age of nation states.

In summary: The Second World War, in fact, demoralized the European colonial masters, provided momentum to the anti-colonial attitudes worldwide and brought dramatic change of the ideological base from colonialism to freedom-freedom of nation and the freedom from colonialism.